Radio carrier telephone system



June 8, 3948. L., A. KELLEY 2,442,815

RADO CARRIER TELEPHONE SYSTEM l Filed April 26, 1944 2 Sheets-Sheet l 'Wfs maw/mu 5457 TERM/NM June 8, 1948. A. KELLEY RADIO CARRIER TELEPHONE SYSTEM 2 Sheets-*Sheet 2 Filed April 26, 1944 INVENToR. A 60A Talky Y stiam WDG Nek Patented June 8, 1948 UNITED STATES TENT OFFICE RADIO CARRIER TELEPHQNE SYSTEM Leo A. Kelley, New York, N. Y., assignor to The `Raulaml Corporation, Chicago, Ill., a corporation of Illinois Y20 Claims. l

This invention relates to new and useful improvements in carrier radio telephone systems.

The principal object of the invention is to eX- tend the range of operation of telephone channels in which so-called talk-listen switching is employed.

A further Objectis the provision of relatively inexpensive means for supervising the use of such channels without the necessity ior'listening to the various conversations.

In the drawings:

Fig. 1 is a block diagram;

Fig. 2 illustrates diagramatically apparatus provided at stationsB and C; and

Fig. 3, apparatus at station A, to control automatic switching of calls between stations B and C via station A.

The circuit arrangements are here described in connection with a carrier radio telephone system of the type described in my application, Serial No. 524,819, le'd March 1, 1944, now U. S. Patent No. 2,417,555, where each user has a talklisten switch which must be operated in the course of a conversation. Fig. 1 shows a block diagram of two such systems so arranged as to illustrate the utility of the present scheme in a practical communications network. Four carrier radio telephone terminals are indicated, the details of which were explained in said application. Each terminal comprises voice terminals, Cv, C1, C2, C3, to each of which an intercom station may be connected as, for instance, I1 connected to terminals C1. I1 does not, of course, have to be the same instrument lfor every conversation over the channel of which C1 is the terminal pair. It is contemplated that not only the channel terminating in C1 but all of the channels will be available when idle for connection to any of the intercom stations at a given carrier radio terminal. All the equipment for deriving the indi- Vidual ordinary voice and carrier channels, including `a relay controlled by the talk-listen switch of the intercom (TLR) and circuits, are shown by boxes labeled V, l, 2, 3; V for ordinary voice, l for carrier number one, etc. In some instances, as indicated by SB, Sw, SE, Sc, one of the armatures of a TLR relay with its set of contacts is shown for a purpose which will be presently made clear. The radio transmitter and receiver for each carrier radio terminal are designated T and R, respectively.

Referring to Fig. 1, it is seen that station A comprises two carrier radio terminals, a west terminal and an east terminal. The west terminal communicates with the terminal at station B via a radio link 'which may include one or more radio relay stations. Similarly, the east terminal communicates with the terminal at station C via another radio link. intercom stations at station A may converse with intercom stations at station B via the west terminal or with station C via the east terminal. in a network of this kind it is often desirable for an intercom at "station B to be able to converse with an intercom at "station C via the west terminal and east terminal at station A. It would be possible, but in most cases it would not be satisfactory, to have a person at station A repeat the conversation in each direction. One of the advantages of the present arrangement is that it makes this conversation vpossible without the intervention or assistanc'eof any person at station A during the conversation. As will be explained below, nothing more is required at station A than that a simple electrical connection be made prior to the conversation.

In Fig. 1, intercom I1 at station B is assumed to be in conversation with intercom I2 at station C via station A. By way of illustration, Ii is connected with carrier channel number one and I2 with carrier channel number two, and a twowire patching cord P is used to connect the C1 of the west terminal with C2 of the east terminal. With the arrangements about to be vdescribed a patching cord P connected between the proper C terminals of the west terminal and east terminal at station A is all that is necessary to permit conversation between any intercom connected to any C terminal at station Band any intercom connected to any C terminal at station C. Y

Assume that the person at I1 wishes to speak. Preparatory to speaking he moves the talk-listen switch to the talk position. This causes the TLR relay of carrier channel number one to become energized. Consequently, SB leaves its lower contact and touches its upper contact, and T at station B is put on the air. Thus, the voice currents from I1 modulate the carrier current of carrier channel number one in carrier branch I, the resulting lower side band modulates the radio wave in transmitter T, and the modulated radio wave is radiated. Radio receiver R at West terminal of station A receives the modulated radio wave and converts it to a facsimile of the original lower side band. All the TLR relays at station A remain de-energized since it is assumed that no one at station A is assisting in ythis operation and no means has yet been described whereby a switching operation at one carrier radio terminal will cause a switching operation at the distant carrier radio terminal with which it is working. This being so, Sw and SE are both in the deenergized position; i. e., connecting the carrier channel apparatus to the output of the associated radio receiver in each case. Therefore, the reproduced side band coming out of R of the West terminal can pass to the carrier apparatus of I. A facsimile of the original voice currents comes out at C1 and goes to carrier channel 2 of east terminal via patching cord P. In carrier channel 2 the reproduced voice currents modulate the carrier current appropriate to that channel and deliver the lower side band product to the armature of SE. However, SE establishes connection with the output of R of east terminal and the energy of the lower side band is dissipated in the output circuit of R.

It is clear that, under these circumstances, no radio wave modulated with the carrier side band will be radiated from the antenna associated with T of "east terminal of station A toward station C" and, therefore, I2 at "station C will not be able to reproduce the words spoken at I1 of station B.

The same situation exists for transmission in the opposite direction in which case the speech originates at Iz of station C and the lower side band is'dissipated in the output circuit of R of west terminal at station A by reason of the position of Sw.

In accordance with the present invention this inoperative condition is overcome by causing the appropriate switching operations to take place automatically at station A. Auxiliary apparatus and connections are provided in one or more channels of the terminals local to the intercoms which, in Fig. 1, includes one or more channels at station B and station C. This apparatus and these connections are shown in Fig. 2.

Furthermore, certain cooperating apparatus and connections are provided in one or more pairs of channels of the terminals where two or more simple carrier radio telephone systems terminate and it is desired to repeat automatically from a channel in one system to a channel in another system. This apparatus and these connections are applicable at station A of Fig. 1, for example, and they are shown in Fig. 3.

Fig. 2 is shown with particular reference to a carrier channel. The slight modification for an ordinary voice channel will be pointed out later. For the purpose of showing how the added apparatus functions with the apparatus of a carrier channel of my prior application, a signicant portion of a typical carrier channel is included in Fig. 2 and as much of an intercom set as is necessary for explaining the invention. Thus, TF is a transformer corresponding to similar transformers in said application. Its left-hand winding is connected to a combined modulator and demodulator MD. The midpoint of this same winding is connected by the wires 2 and I to the output of carrier oscillator O within the dashed rectangle. The details shown for O are merely by Way of example. Attention is principally directed to the condenser Ct which is an important factor in determining the frequency of the current generated by the oscillator. The right-hand winding of TF is connected to the left-hand terminals of a band pass filter BF. The ungrounded side of this connection is made through the series connection of the upper armatures and their nQlmally closed contacts of the relays RL1 and RLz, as shown. The ungrounded right-hand terminal of BF is connected to the armature of the TLR relay associated with the channel for the purpose of switching the channel between the radio receiver R and the radio transmitter T. It can readily be seen, therefore, that the normal operation of the channel is not affected so long as the relays RL1 and R132 remain de-energized.

The upper armatures of relays RL; and RM also have normally open contacts which are connected in parallel and, by the wires 3 and I, to the output of the carrier oscillator O, as shown. Relays RL1 and RLz also have lower armatures which are connected in parallel and to the ungrounded side of the oscillator tuning condenser Ct. Each of the lower armatures has a normally open contact, that of RL1 being connected to the ungrounded side of condenser C and that of RLQ to the ungrounded side of Cb. The grounded sides of Ca, Cb, and Ct are, of course, all connected together.

When relay RL1 is energized its upper armature moves to the normally open contact and thereby connects the output of the carrier oscillator directly to the ungrounded left-hand terminal of BF and opens the circuit looking back to TF and MD by reason of the armature leaving the normally closed contact. At the same time, the lower armature of RL1 moves to its normally open contact and thereby connects condenser Ce. in parallel with the oscillator tuning condenser Ct. Similarly, if relay Rlla is energized instead of RL1, its upper armature moves and makes the same connection and disconnection that the upper armature of RL1 did, and its lower armature connects condenser Cb in parallel with oscillator condenser Ct.

It is well-known that when a condenser is connected in parallel with the tuning condenser of an oscillation generator, the frequency of the oscillations generated is lower than it was before the connection was made. Prior to the energizing of either RL1 or RLz the carrier oscillator is generating at the normal carrier frequency for that channel and is supplying its output to the combined modulator and demodulator MD in the normal way. When RL1 is energized, the oscillator generates at a lower frequency depending upon the capacity of Ca and supplies this lower frequency output directly to the left-hand terminals of BF. Ihe same is true when RLz is energized except that the lower frequency is different if the .capacity of Cb ls different from that of Ca, and it is different in the present apparatus.

In order to make this more concrete, the following numerical example is offered: The capacity of Ca is of such value that it lowers the carrier frequency by the amount of 900 C. P. S., and that of Cb so that it lowers the carrier frequency by the amount of 600 C. P. S. In carrier channel number one, with a carrier frequency of 5900 C. P. S., connection of Ca causes the oscillatorto generate at a frequency of 5000 C. P. S. and connection of Cb causes the oscillator to generate at a frequency of 5300 C. P. S. The band filter BF in this carrier channel transmits, with little loss in the frequency range, 3100 to 5700 C. P. S. Consequently, the currents of lowered frequencies 5000 and 5300 C. P. S. are readily transmitted through BF when the output of the oscillation generator, operating at either of these lowered frequencies, is connected directly to the left-hand terminals of BF. If, at this time, the relay connected with the first channel is energized so as to connect the right-hand terminals of BF to the radio transmitter 4'11, a radio wave modulated by the current of frequency 5000 or 5300 C. P. S. is radiated toward the distant terminal radio receiver where a facsimile of the current of frequency 5000 or 5300 C. P. S. enters the number one carrier branch there, intermodulates in the combined modulator and demodulator with the carrier -oscillatorvcurrent at 5900 C. P. S. and sends on to theC1 terminals a current of 900 or 600 C. P. S., the 900 C. P. S. being the dilerence between 5900 and 5000 C. P. S., and the 600 C. P. S. the difference between 5900 and 5300 C. P. S. The currents of 900 and V600 C. P. S. are utilized at the distant terminal for performing switching operations which will be described in connection with Fig. 3.

It is suiiicient to state at this point that the 900 C. P. S. current will cause the appropriate 'I'LR relay to become energized and the. 600 C. P. S. current will cause that TLR relay to -become de-energized. This statement may be made clearer by yputting it in terms of the illustration of Fig. l. If the apparatus of Fig. 2 is assumed to be connected with the carrier channel number one at station B, then the 900 or 600 C. -P. S. current williiow in the portion of the system at station A where the designations C1, P, C2, appear. It will be recalled that in explaining the operation in the absence of automatic switching at station A, it was pointed out that when a person at I1 (station B) endeavored to talk with a persen at I2 (station 0) via the patch cord P (station A) he could not do so because the TLR relay of carrier channel number two of the east terminal at station A remained deenergized and, as a consequence, its armature SE remained on the contact which connects the channel with the output of the radio receiver. If this TLR relay could be energized, the armature SE would move to the contact which Vconnects the channel with the radio transmitter, and the person at I1 (station B) could talk to the person at I2 (station C). A replica of the voice currents produced by I1 station 15) would be supplied to carrier channel number two (east terminal of station A) via its C2 terminals, the resulting lower side band current from channel two would iiow via SE (now assumed Operated to the lower contact) to radio transmitter T ("east terminal) where it would modulate the radio wave. the modulated radio wave would be radiated and picked up by the antenna at radio receiver R (station 0) and demodulated in R,

the resulting lower side band would pass via Se f to carrier channel number two, and nally afacsimile of the voice currents produced by I1 (sta tion B) would ilow via terminals C2 to I2 (sta tion C). It may be seen then that ii the 'ILRz relay of east terminal at station A is energized at the same time that the TLR1 relay of station B is energized as a result of operating'the switch at I1 to the talk position, I1 (station 13) can talk through to the person at 'I2 (stati on C). The requirements for talking through in the opposite direction are exactly similar.

The 900 C. P. S. current which ilows in the portion C1, P, C2 of thesystem at station A a result of the operation of relay RLi associated with carrier channel number one at station B cause the TLRz relay (east terminal vat station A) to become energized by virtue of the circuit arrangement of Fig. 3. rIhe arrangement of Fig. 3 also provides for the de-energizationv of then the person at` rent flowsin the same portion of the system. A

detailed description of Fig. 3 follows after the explanation of Fig. 2 is completed.

IIt must be apparent now that the operation of the relays RLi and RLz should depend upon the operation of the talk-listen switch of the associated -local intercom station. Operation of the RLi relay causes the energizing of a particular TLR relay-at va remote station associated with a diierent terminal-to-terminal carrier radio telephone system, while operation of the companion RLz relay causes the de-energization of the same TLR relay. 'In the present arrangement, the RLi relay is energized momentarily when the talk-listen switch is first moved to the talk posi-tion and the RLz relay is energized momen-- tarily near the first part of the movement of the talk-listen switch as it returns to the listen position. As a practical matter, momentarily means less than a fewtenths of a second.

yInliig. 2, one simple way in which the momentary 'operation of relays RL1 and RL2 may be secured, is shown. The winding of relay RLs is connected in an energizing ycircuit controlled by one of the stationary and movable contacts on thetalk-listen switch T-L, similar to the arrangement described in said application for energizing the TLR relay. When the relay RLa is energized by moving the talk-listen switch toward the "talk lposition, its armature A moves to its lower contact completing a circuit including,

`in series, the source of unidirectional voltage B,

resistance R, condenser C, and the two branches in parallelrcomprising in onebranch the rectier RE; and the winding of relay RLi, and in the other branch the rectifier REz `and the winding of relay RLe, and return paths via ground to the other side of B. The rectifiers RF1 and REZ are conductive in one direction only. In Fig. 2, they are oppositely poled with respect to the the source B. As soon as armature A touches the lower contact, a momentary unidirectional current iiows, Icharging condenser C. Rectiiier RE1 is so poled as to be conductive to this current so that relay RL; is momentarily energized. At this time relay RLz is not energized because rectiiier REg is so holed as not to be conductive to this current. However, when the talk-listen switch is released to the listen position, vcondenser C discharges Vvia armature A to ground. The discharge is also momentary and opposite in direction to the charging current. Therefore, rectifier REZ is conducting to the exclusion of RE1, and relay RLz is momentarily energized. The factors controlling the magnitude, shape and duration of these current pulses are well-known and hence will vnot be further discussed. Other simple or more elaborateV circuits may be employed for this purpose in lplace of the one shown in Fig. 2.

,In order to insure that the operation of RL2 will take place while the armature of the TLR relay still connects the carrier channel to the radio transmitter T-so that the signal created by "the operation of RLz will be radiatedthe -pointsin the travel of the talk-listen switch where relays TLR and R-L3 are energized should be displaced by an ample margin. That is, relay TLR Ashould be energized near the first part of the movement lof the switch from listen to talk and Yrelay RLs near the end of this movement. To the same end, the TLR, relay may be made to `have a quick make and slow release.

Fig. 3 consists Aof two similar shunt circuits, one-of-which is-shown in detail. These circuits are connected in shunt to the C terminals at a station, such as station A of Fig. 1, where the voice terminal-s of more than one carrier radio telephone system -are located and it is desired to repeat automatically from one system to another system by means of a patching cord such as P. In Fig. 3 the circuit shown in detail is connected in shunt to the C terminals of an east branch and such circuit is responsive to signals emanating from a channel associated with the remote terminal in the system toward the west. It should be noted that Fig. 2 may be applied to any or all of channels I, 2 and 3 at station B, and that the switching signals flowing to corresponding terminals C1, C2 and Ca of the west terminal at station A will, in each case, consist of a spurt of current of either 900 or 600 C. P. S. Consequently, when any one of the C terminals of west terminal is patched to any C terminal of east terminal, the latter is supplied with a spurt of 900 C. P. S. current just prior to talking west to east, and a spurt of 600 C. P. S. current just after the talking in this direction ceases. The detailed shunt circuit is, therefore, typical of the apparatus associated with each channel of the east terminal." The uncompleted shunt circuit in Fig. 3 connected across the C terminals of a west branch is intended to provide similar switching operations from station C via any channel to the east terminal at station A, thence via a patching cord to -any channel of the west terminal at station A to station B. Except for details relating to the frequency of the signal pulses, the two shunt circuits are the same, so a detailed explanation of the shunt circuit connected across the C terminals of an east branch will be given as typical for both shunt circuits.

Referring to Fig. 3, the shunt circuit for west to east operation starts at the place where it is connected across the C terminals of an east branch. It goes rst to a transformer TF1 comprising two primary and two secondary windings. The rectangular symbol marked L indicates a magnetic shunt or high flux leakage path between the two sets of primary and secondary windings, the sets being taken in the sense that the upper primary and upper secondary windings constitute one set, and the lower primary and lower secondary the other set. The transformer may consist in fact of two transformers, one for each set, or a single unit may be constructed using shell-type laminations and putting one set of windings on one outside leg, the other set of windings on the other outside leg, leaving the central leg unwound. In the latter case, the central leg would constitute the magnetic shunt indicated by L in Fig. 3. The advantage of thus magnetically separating the windings will become clear as the description proceeds. In practice, the primary windings may be alike and, likewise, the secondary windings; in other words, effectively two identical transformers.

Each secondary winding is tuned to a particular frequency by means of a shunt connected condenser, the lower secondary being tuned to a frequency of 900 C. P. S., and the upper to a frequency of 600 C. P. S. The magnetic shunt assists greatly in making the tuning of the secondaries independent of each other. This is further aided by the connection of a high resistance RT in series with the primary circuit. The resistance value of RT is made high with respect to the reactance of each primary winding which,

when talking in the east to west direction; i. e.,l

as noted, may be the same in practice, at -the signal frequencies, in this case 900 and 600 C. P. S. This improves the sharpness of tuning in the respective secondary circuits. Usually the resistance value of Rr, thus determined, will be much larger than the impedance level over the voice frequency range in the branch circuit (see Fig. 3, any east branch) before the shunt circuit is connected. In case it is not, it should be made so in order to reduce the shunting effect of the added circuit to a negligible magnitude.

The secondary windings are each connected between the control grid and cathode of a triode. They are given many more turns than the associated primary windings in order to secure a substantial voltage set-up. The lower secondary winding tuned to 900 C. P. S. is connected between the input electrodes of tube V1, while the upper secondary winding tuned to 600 C. P. S. is similarly connected with tube V2. A negative grid bias is applied between the control grids and cathodes of 4these tubes, as shown by the battery Bc, suii'cient to cause plate current cut-off in both tubes when no signal is being received. It is evident that a current of 900 C. P. S., picked up by the shunt circuit, will excite only the lower secondary which is tuned to 900 C. P. S., and when this happens a current will flow in the plate circuit of V1 only. Similarly, a current of 600 C. P. S. will cause a current to flow in the plate circuit of V2 only. In the plate circuit of each tube, a by-pass condenser is connected so that substantially only direct current flows for the duration of the 900 or 600 C. P. S. signal, as the case may be.

The direct current component of the plate current of V1 is made to flow through the righthand winding of relay RLc. Recalling that operation of the talk-listen switch to the talk" position at station B causes a spurt of 900 C. P. S. current to flow in the circuits joined by the patching cord (at station A) and, therefore, in the shunt circuit now under consideration, it is clear that this operation of the talk-listen switch causes a pulse of direct current to flow through the right-hand winding of rel-ay Rllc, energizing it momentarily. When this happens the armature of RIc moves against its normally open contact and thereby completes a number of circuits, each including the voltage source connected between ground and the armature contact, as shown in Fig. 3. One of these completed circuits comprises, in series, the volt-age source, the left-hand winding of RLc, a resistance for controlling the current in this circuit, and the armature and its normally closed contact of another relay RL4, the circuit being completed via ground. This is a locking circuit for RLc because, once this circuit is closed by the pulse of current through its right-hand winding, the relay is maintained energized by current flow through the left-hand winding in this circuit until it is later broken by the energizing of relay RL4. In addition to closing the locking circuit, the voltage source is also connected to energize relay TLR2 of the east branch to which this shunt circuit is connected. The voltage source is also connected by the operation of RLc so as to light a supervisory lamp or the like, indicating to an attendant that the circuit is in use for talking in the west to east direction.

At the end of the talking period, the talk-listen switch at "station B is released. At this time, as already explained, a spurt of 600 C. P. S. current is caused to flow in the circuits joined by 9 the pat-ching cord (gat staton A) and hence in thefshunt circuit of Fig. 3. This causesa pulse of current in the; platecircuit of V2,; the direct comoponent ofk which ows through lthe winding of relay RL4; energizingit momentarily; rIhis causes the armature or to leave its contact brieiy, but in so dong-itopensthe holding circuit of the'leftehand windingof RLsiwhich becomes and remainsdeenergized` until thereceipt ofthe next 900 C. P. S. currentspurt. When the relay` EL3 becomes dre-energized; itsy armature moves away from the contact' to which the voltagesup ply is connected, and thus de-energizes all the circuitstowhichA the armature is connected. Of these, the holding'winding circuit'has beenvnoted. In addition, the. TLR relayy is de-energized" and the: supervisory lamp goes out;

The net result of the operations described in the'prece'ding'two paragraphs is. to use the illustration ofV Fig. 1; that the person'at I1 (station 13)` is able by the manipulation oi his talk-,listen switch to control'not only the'I'LR.`V relay represented by Si;- at station B but also the TLR relay representedby SE a't the east terminal of stationA. When he moves his switch to the talk position, both SB and SE move, appropriately for talking to I2 at station C, to connect the associated carrier channels with their respective-radio transmitters and,-when he releases his switch to the listen position both SB and SE' move, Vappropriately for listening to I2 at station backY to the positions4 shown in Fig. 1, where they connect the associated carrier channels with theiryrespectve radio receivers.V It is obvious that this is typical of the control which can be effected at station B over any carrier channel equipped with the apparatus of Fig. 2 upon any channelv of thevcarrierradio' telephone system` comprising the east terminal at station A and-*the terminal at station C which is equipped with the apparatus of Fig. 3 at the' east terminal.

Similarcontrol canbeV exercised on any carrier channel at station'C by equipping such channel With-the apparatus of Fig. 2. In thiscase, however,4 it visnecessary to use' currents of different frequenciesfrom-those' employed forwest to east control. Referring to Fig. 2, for example, the capacity of Ca'is new of such value as to lower the normal carrier frequency by 1500 C. P. S. and the capaci-ty ofl Cb to lower thenormal carrier frequency by 1200 C. P. S. Consequently, when the --person I2 Y(station C) moves his` switch to thetalk position, a spurt of 1500 C. P. S. current owsvia vthe terminal C1 at the "west" termina atstation A, and when he releases his switch to the listen position, a spurtl of 1200 C; P. S1.' current flows. Referring to Fig. 3, the uncompleted shunt circuit connected across the branchdesignated any west' branch is responsive to these' 1500 and 1200' C. P. S. switching signals. The details of this shunt circuit are preciselythesame as for'the shunt circuit shown for the-900 and 600 C. P. S. switching signalswith the exception that the'A transformer' secondaries aretunedfor1500 and-1200 C. P. S. instead of 900 and-600 C;P. S.; respectively, and, ofcourse, the associated TLR relay of al west branch instead 'of an'eastrbranch is energized upon'the operation of theV correspondingA relay to Rlc. Therefore, the person at Iz (station C) can control the east;totwest talkingv circuit by controlling the TLRgrelay at"station C represented vby Se andl the TLR relay at west terminal of station A represented loy Sw;

Ifhuatne persensat I r fstatien B an d I2 statien3l can. eenverse with each. otherby. joininetneir. channels. with a .patching Gerd, 12 and without the further assistante of. any person 5 at statien .The .switching signals being momentary do net interferewith thenSe .of the Circuit fer eenversetien.. Eurthermere... an, attendant at station A byobservine thesuper: visery lamps for particular.patehinsteenneetion 1o will know whentto remove the patching cord and.

free the. channels for. the. use of others.. not only for eenversatiensbetween station B and fstati-on' C but also from station A to either station B or station C.",

15 .It mentienedear 1er. that .theeleit.Of Fig., 2 should be slightlymodied for the ordinary veee Channel- The reasongforthisis 4that ani es eillater is required to generate the switching Signal currents. Ineaehpfthe carrier channels all esellater isready at hand in theiorm ofthe carrier oscillator.n The arrangementiof- Figi? makes use orftitlecarriery oscillator but,; as `no Carrier oscillator is used in the ordinary. yo'ce ehanne1, i t i s nee es.s a ry .to supply one. Therefore,a separaten, oscillator isnsuplpliedin-theordif nary. veiee .Channel for oscillator OA of Iig.

W i re 2 isgenitted fenobyious reasons. condene ser. Cttunes. theeseillatorto a frequency of .900 C- .R- S Cendensera andthe lewerarmaturefof relayRLi aregomitteci., l,(3 onjdenser C213 has a value 0f eapaeitr which lowersthe frequency ofthe eseillaterto 600 CLR- relaynhz is enereihed.. Infall other respeets n.12. is the same as fenany. earner ehanne1. '.lhe'sgnalfrequeneies 01.9.00.and600-C-- BS. applyrof course; G O.Stav tien. BLS?- .At statien C .the se frequencies are 150.0 and 112002C. .1?. S ,re.spe e tive1y.i

este Eis. 3l the arrangementisprecisely the same forthe ordinary voice channels asit i's'for 40 each carrier channel. Manyvariations ,and extensions of the arrangem'entshere d eseribediwilloccur .tn thosesknled inzthis; art., Forinstancefstation A maybe the' feealpent .110.11 mere. thantne .two carrier radio telephenesystemsgshowh in Eig.. .1. Communicatienlnayhe had .fromone outlyngstat'en to any other. eutlxrngtaton va. station A employing' eirenit. arrangements. @f the character described. Alsogrthe Y-shunt cirQuitsoFg. 3 maybe assoeatedwth. the veordicircuits vrather than the individual branch circuits,j in whichjcase provision should be made Afor connecting-'in thezwinde ing of4 the proper, TLB. relay when plugging.` in. 'Ifubesl/Trganil/z' of Fig 3. may' be' of. other than the triode type'with appropriate circuit altera;V

tions. The arrangement of Fig. 3 may be co'r'n bined with 'that of 2 at a'single'stationfr Control-ung the switchingeperatiohs" atstiirain othersta'tion: Theparueruiafr van' 00' any case' will usually 'defpnfd upor rth an meant ef atterrare' temeraria ahd" ,t he character o'fV the telephone' service desired.`V n

, todes gnj erneans'forestablishm-g andrserving L quencylspectrum-for the transmission of elecv tricalsignals. Wm V WhatI elairnisr v1. AI n aY carrier radio Itelephone system,` two terminal stations;` each havinga radio transmitter-and receiver, a plurality'of 'two-way'channels in the ether lor' ona'wphysieaiiiheja at each station; a setconsisting-'01" a; telephone` and a two-position switch, means for connecting the set with a channel of the first station, means responsive to the movement of the switch into one position for connecting the iirst and the second station with their associated transmitters, and means responsive to the movement of the switch into the second position for connecting said stations with their associated receivers.

2. The system according to claim 1, and a relay at the first station having a circuit controlled by said switch, means at the first station for sending distinctive signals to the second station in the two positions of the switch, and a relay at the second station responsive to said signals.

3. The system according to claim 1, a relay at each station for alternately connecting the station with the associated transmitter and receiver, a circuit for the relay at the rst station controlled by the switch, means for sending distinctive signals in each position of the switch, and a circuit for the relay at the second station responsive to said distinctive signals.

4. In a carrier radio telephone system, two terminal stations, each havin-g a radio transmitter and a receiver, a plurality of two-way channels at each station, a set consisting of a telephone and a two-position switch adapted to connect the telephone with a channel at the first station for talking and listening, means operative in the talking position of the switch for connecting the first station to the associated transmitter and for transmitting a first signal, means operative in the listening position of the switch for connecting the rst station with the associated receiver, and for transmitting a second signal, and means at the second station responsive to the first signal for connecting it with the associated transmitter and responsive to the second signal for connecting it with the associated receiver. l

5. In the system according to claim 4, a relay at each station for alternately connecting the station with the associated transmitter and rreceiver, means at the first station operable when the switch is moved into the talking position for rst energizing the associated relay and then producing a first signal, means at the rst station operable when the switch is moved into the listening position for producing a second signal while the transmitter is connected with the station and then connecting the station with the associated receiver, and a circuit for the relay at the second station responsive to the rst signal to connect the station with the associated transmitter and to the second signal to connect it with the receiver.

6. In a carrier radio telephone system, four terminal stations, each having a radio transmitter and receiver, a plurality of two-way channels at each station, a telephone for each channel at the rst and second stations, means for establishing two-way communication between channels at the iirst and second stations over channels at the third and fourth station, including a twoposition switch for each telephone connecting in one position the associated channel with the telephone for talking and in the second position for listening, a vfirst means for each channel for connecting the associated channel alternately t the receiver and the transmitterat the terminal station, a second means for certain channels, means operative in the talking position of the switch for operating the first and second means of the associated channel, means for connecting achannel of the third station with a channel of the fourth station, and means controlled by a second means'for operating the ilrst means of the last-mentioned channel.

7. Ihe system according to claim 6, and in which the iirst means is a relay whose circuit is closed in the talking and opened in the listening position of the switch,l and contacts'for the 'relay for connecting the telephone of the associated channel with the transmitter of the associated station in the talking position, and with the receiver in the listeningl position of the switch.

8. The system according toclaim 6, and in which the second means is a relay whose circuit is closed in the talking and opened in the listening position of the associated switch.

9. The system according to claim 6,'and in which the first means comprises a relay connecting over a back contact with the associated receiver and over the front contact with the associated transmitter, and means operative in the talking position of the switch for energizing the relays at the rst and fourth stations.

10. The system according to claim 6, and means controlled by the switch for 'successively operating the first and second means of the associated channel when it is moved into the talking position.

11. The system according to claim 6, and in which the'iirst and second means are relays, and the second relay is energized when the switch is moved into the talking and de-energized when it is moved into theV listening position, means for energizing the first relay of the connected channel of the fourth station in response to the energization and means for de-energizing it upon the de-energization of said second relay.

l2. The system according to claim 6 and in which the last-mentioned means comprises means for sending a signal of a predetermined frequency to operate the first means associated with the connected channel of the fourth station to connect with the associated transmitter.

13. The system according to claim 6, and in which the last-mentioned means comprises means for sending a signal of a predetermined frequency to operate the first means associated with the connected channel of the fourth station to connect with the associated receiver.

14. The system according to claim 6, and in which the last-mentioned means comprises means for transmitting a signal of a predetermined first frequency when the switch is moved into the talking position and a signal of a predetermined second frequency when the switch is moved into the listening position, and means responsive to said first frequency for operating the first means of the connected channel of the fourth station to connect the channel with the associated transmitter and means responsive to the second frequency for operating the last-mentioned first means to connect the channel with the associated receiver.

15. In'a multiplex radio communication system, Vtwo terminal stations, each comprising a radio transmitter and receiver, a plurality of carrier channels at each station, each carrier channel containing an oscillator and a modulator, the oscillator of each channel being arranged to generate a carrier of different frequency, a relay at each station 'for controlling the alternate connection of a given channel at each station to the associated transmitter and the receiver, a telephone, a switch for connecting the telephone with a channel'at the first station for talking and listening purposes, a circuit forthe relay 13 at the rst station controlled when the sWitch is moved towards the talking position, means controlled by the switch for operating said oscillator to produce a distinctive signal, and a circuit for the relay at the second station responsive to said signal.

16. The system according to claim 15, and in which said oscillator comprises tuning means, means responsive to the moving of the switch to the talking position for momentarily Varying the tuning of the oscillator of the connected channel to a predetermined extent, means responsive to the moving of the switch to the listening position for momentarily varying the oscillator of the connected channel to a different extent.

17. The system according to claim 15, and in which the switch when moved to the talking position momentarily varies the tuning of the oscillator of the channel with which the telephone is connected to a predetermined extent, and when moved to the listening position momentarily varies the tuning to a different extent, two tuned circuits at the second station responsive, respectively, to signals produced by the momentary variations in the tuning of the oscillator, and means controlled by said tuned circuits for controlling the circuit of the relay at the second station.

18. The system according to claim 15, and in which the switch when moved to the talking position momentarily varies the tuning of the oscillator of the channel with which the telephone is connected to a predetermined extent, and When moved to the listening position momentarily varies the tuning to a diierent extent, two tuned circuits at the second station responsive, respectively, to signals produced by the momentary variations in the tuning of the oscillator, a second and a third relay at the second station, an energizing circuit closed for the second relay by the tuned circuit responsive to the movement of the switch into the talking position, and an energizing circuit closed for the third relay by the other tuned circuit, a locking circuit for the second relay controlled in a back contact of the third relay, the circuit of the rst relay at the second station being controlled in a front contact of the second relay.

19. In a multiplex radio communication system, two terminal stations, each comprising a radio transmitter and receiver, a plurality of carrier channels at each station, each carrier channel containing an oscillator and a modulator,

the oscillator of each channel being arranged to generate a carrier of diierent frequency, a rst relay at each station, multiple connections from the channels at each station to the associated transmitter and the receiver controlled by the associated relay, a telephone, a two-position switch for connecting the telephone with archannel at the rst station, in lone position for talking and in the second position for listening, a circuit for the relay at the rst station closed when the switch is moved towards the talking position, a second relay at the rst station, a circuit for the second relay closed by said switch when moved towards the talking position after the energization of the first relay, means controlled by the second relay for operating the oscillator of the channel with which the telephone is connected to produce a distinctive signal, and a circuit for the iirst relay at the second station responsive to said signal.

20. The system according to clain 19, and in which said oscillator comprises a tuning condenser, a rst signaling relay, means controlled thereby for connecting a condenser of a predetermined value in parallel with the tuning condenser, a second signaling relay, means controlled thereby for connecting a condenser of a diierent predetermined value in parallel with the tuning condenser, said signaling relays having parallel circuits, oppositely poled rectiers in the individual branches of said parallel circuits, a condenser and a resistance in a common branch of the parallel circuits, an armature controlled by the second relay in the common branch of said circuits for alternately connecting it to ground and battery, the elements of said parallel circuits being so proportioned that in one position of the armature one signaling relay and in the second position the second signaling relay is momentarily energized.

LEO A. KELLEY. y

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 899,242 Cabot Sept. 22, 1908 1,689,026 Heising Oct. 23, 1928 1,709,044 Smythe Apr. 16, 1929 2,292,222 Haigis Aug. 4, 1942 

